Eyeglass lenses and other transparent plastic materials are subject to becoming dull and hazy due to scratching and abrasion during use. Polycarbonate eyeglass lenses, for example, while strong and shatter-resistant, also have relatively soft surfaces that are susceptible to scratching.
Various coatings have been proposed for eyeglasses and other transparent plastic materials to reduce their propensity to become scratched and abraded. One such composition is shown in U.S. Pat. No. 4,378,250 (Treadway et al.), granted Mar. 29, 1983. This patent shows the use of a coating composition that has two basic components, one being an at least partially hydrolyzed epoxy-functional alklyalkoxysilane and the other a derivative of an amine-substituted alkyltrialkoxysilane, also at least partially hydrolyzed. The amine component is reacted with a carbonyl compound such as a ketone to form, for example, an imine structure which stabilizes this component. The coating composition itself is formed by mixing together the two components, permitting the mixture to stand for a period of time, and then using the resulting material to coat eyeglass lenses or the like.
U.S. Pat. No. 5,866,262 (Galic et al.), granted Feb. 2, 1999, discloses a coating composition that employs two components that appear to be substantially identical to the components employed in the Treadway et al. '250 patent except that it is said that the components are fully hydrolyzed. Galic et al. explain that "fully hydrolyzed" means that the hydrolysis reaction involving the three alkoxy groups pendant from the silicon has been conducted in the presence of at least a stoichiometrically sufficient amount of water to hydrolyze all of the alkoxy groups. The Galic et al. composition requires "bodying", explained as a copolymerization reaction which occurs as the mixture of the two components is permitted to stand for a period of time. It has similarly been found that with the Treadway et al. '259 coating composition, if "bodying" is not carried out following mixing together of the two silane components, a coating of the material on a transparent substrate will tend to undergo "mudcracking" as the composition dries. Mudcracking refers to a phenomenon in which the coating itself develops a series of odd angled and completely unacceptable cracks similar in appearance to the cracked surface of dried mud flats. The appearance of mudcracking in coating compositions containing the hydrolysis products of an epoxy alkoxysilane and an imine derivative of an amino alkoxysilane does not appear to be dependent upon whether the compositions have been partially or fully hydrolyzed.
The necessary "bodying" procedure of a coating composition tends to substantially reduce the pot life of the composition--that is, the time the composition can be maintained at room temperature and optical lenses, for example, can be dipped or otherwise successfully coated with the material. If the bodying procedure could be avoided, the pot life of the coating composition could be substantially increased, and this would represent a substantial benefit by reducing the per lens cost of the coating material and reducing the frequency with which new batches of the coating composition need to be prepared.